1. Field of the Invention
The present invention relates to a method of producing a hollow particulate material. In particular, the present invention relates to a method of producing hollow particulate materials having varieties of compositions and structures through simplified steps.
2. Description of Related Art
Hollow particulate materials have been developed and placed on the market as functional materials that are light-weight, have heat insulating properties, and can scatter light. Unfortunately, traditional methods of producing hollow particulate materials are complicated. For example, seed particles are prepared and then polymerized; water-in-oil (W/O) emulsion is prepared and then converted into water-in-oil-in water (W/O/W) composite emulsion; and/or thermally expandable microcapsules having thermoplastic polymer sheathes containing low-boiling-point liquid therein are prepared and then thermally expanded.
Aside from these techniques, inventions have been made which are directed to simplified production of hollow particulate materials using gas as a template. For example, Japanese Patent Application Unexamined Publication No. 2011-245452 discloses a technique involving polymerization of gasified polymerizable monomer at the interface between the gas phase and the liquid phase; Japanese Patent Application Unexamined Publication No. 2007-21315 discloses a technique involving polymerization of a substance at the surfaces of bubbles in liquid; and Japanese Patent Application Unexamined Publication No. 2007-196223 discloses a technique involving acceleration of polymerization of a substance in a liquid phase with a catalyst in a gas phase.
Since precursors of the hollow particulate materials are formed after formation of bubbles having unstable structures in these techniques, hollow particulate materials cannot be produced stably. In addition, a vaporizable and polymerizable monomer is essential for the technique disclosed in Japanese Patent Application Unexamined Publication No. 2011-245452; a polymerizable substance that can selectively adsorb on the surfaces of bubbles is essential for in Japanese Patent Application Unexamined Publication No. 2007-21315; and a vaporizable catalyst is essential for in Japanese Patent Application Unexamined Publication No. 2007-196223. As a result, very limited substances can be used for production of hollow particulate materials.